Joint Space Science Institute JSI

College Park, MD, United States

Joint Space Science Institute JSI

College Park, MD, United States
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Schnittman J.D.,NASA | Schnittman J.D.,Joint Space Science Institute JSI
Physical Review Letters | Year: 2014

We present a new upper limit on the energy that may be extracted from a Kerr black hole by means of particle collisions in the ergosphere (i.e., the "collisional Penrose process"). Earlier work on this subject has focused largely on particles with critical values of angular momentum falling into an extremal Kerr black hole from infinity and colliding just outside the horizon. While these collisions are able to reach arbitrarily high center-of-mass energies, it is very difficult for the reaction products to escape back to infinity, effectively limiting the peak efficiency of such a process to roughly 130%. When we allow one of the initial particles to have impact parameter b>2M, and thus not get captured by the horizon, it is able to collide along outgoing trajectories, greatly increasing the chance that the products can escape. For equal-mass particles annihilating to photons, we find a greatly increased peak energy of Eout≈6×Ein. For Compton scattering, the efficiency can go even higher, with Eout≈14×Ein, and for repeated scattering events, photons can both be produced and escape to infinity with Planck-scale energies. © 2014 Published by the American Physical Society.


Cackett E.M.,Wayne State University | Zoghbi A.,University of Maryland University College | Zoghbi A.,Joint Space Science Institute JSI | Reynolds C.,University of Maryland University College | And 5 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

The recent detection of X-ray reverberation lags, especially in the Fe Kα line region, around active galactic nuclei (AGN) has opened up the possibility of studying the time-resolved response (reflection) of hard X-rays from the accretion disc around supermassive black holes. Here, we use general relativistic transfer functions for reflection of X-rays from a point source located at some height above the black hole to study the time lags expected as a function of frequency and energy in the Fe Kα line region. We explore the models and the dependence of the lags on key parameters such as the height of the X-ray source, accretion disc inclination, black hole spin and black hole mass. We then compare these models with the observed frequency- and energy-dependence of the Fe Kα line lag in NGC 4151. Assuming the optical reverberation mapping mass of 4.6 × 107 M⊙, we get a best fit to the lag profile across the Fe Kα line in the frequency range (1-2) × 10- 5 Hz for an X-ray source located at a height h = 7-2.6 +2.9RG with a maximally spinning black hole and an inclination i < 30°. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Cowperthwaite P.S.,University of Maryland University College | Cowperthwaite P.S.,Joint Space Science Institute JSI | Reynolds C.S.,University of Maryland University College | Reynolds C.S.,Joint Space Science Institute JSI
Astrophysical Journal Letters | Year: 2012

The broad-line radio galaxy 3C120 is a powerful source of both X-ray and radio emission including superluminal jet outflows. We report on our reanalysis of 160ks of Suzaku data taken in 2006, previously examined by Kataoka et al. Spectral fits to the X-ray Imaging Spectrometer and Hard X-ray Detector/positive intrinsic negative data over a range of 0.7-45keV reveal a well-defined iron K line complex with a narrow Kα core and relativistically broadened features consistent with emission from the inner regions of the accretion disk. Furthermore, the inner region of the disk appears to be truncated, with an inner radius of r in = 11.7+3.5 - 5.2 rg . If we assume that fluorescent iron line features terminate at the inner-most stable circular orbit (ISCO), then we measure a black hole spin of at a 90% confidence level. A rapidly spinning prograde black hole () can be ruled out at the 99% confidence level. Alternatively, the disk may be truncated well outside of the ISCO of a rapid prograde hole. The most compelling scenario is the possibility that the inner regions of the disk were destroyed/ejected by catastrophic instabilities just prior to the time these observations were made. © 2012. The American Astronomical Society. All rights reserved..


Kara E.,Institute of Astronomy | Fabian A. C.,Institute of Astronomy | Cackett E. M.,Wayne State University | Steiner J. F.,Institute of Astronomy | And 4 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

Reverberation lags in active galactic nuclei (AGN) were first discovered in the NLS1 galaxy, 1H0707-495. We present a follow-up analysis using 1.3 Ms of data, which allows for the closest ever look at the reverberation signature of this remarkable source. We confirm previous findings of a hard lag of ~100 s at frequencies ν ~ [0.5-4] × 10-4 Hz, and a soft lag of ~30 s at higher frequencies, ν ~ [0.6-3] × 10-3 Hz. These two frequency domains clearly show different energy dependences in their lag spectra. We also find evidence for a signature from the broad Fe Ka line in the high-frequency lag spectrum. We use Monte Carlo simulations to show how the lag and coherence measurements respond to the addition of Poisson noise and to dilution by other components. With our better understanding of these effects on the lag, we show that the lag-energy spectra can be modelled with a scenario in which low-frequency hard lags are produced by a compact corona responding to accretion rate fluctuations propagating through an optically thick accretion disc, and high-frequency soft lags are produced by short light-travel delay associated with reflection of coronal power-law photons off the disc. © 2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Reynolds C.S.,University of Maryland University College | Reynolds C.S.,Joint Space Science Institute JSI | Brenneman L.W.,Harvard - Smithsonian Center for Astrophysics | Lohfink A.M.,University of Maryland University College | And 6 more authors.
Astrophysical Journal | Year: 2012

The analysis of relativistically broadened X-ray spectral features from the inner accretion disk provides a powerful tool for measuring the spin of supermassive black holes in active galactic nuclei (AGNs). However, AGN spectra are often complex and careful analysis employing appropriate and self-consistent models is required if one has to obtain robust results. In this paper, we revisit the deep 2009 July Suzaku observation of the Seyfert galaxy NGC3783 in order to study in a rigorous manner the robustness of the inferred black hole spin parameter. Using Monte Carlo Markov chain techniques, we identify a (partial) modeling degeneracy between the iron abundance of the disk and the black hole spin parameter. We show that the data for NGC3783 strongly require both supersolar iron abundance (Z Fe = 2-4 Z ) and a rapidly spinning black hole (a > 0.89). We discuss various astrophysical considerations that can affect the measured abundance. We note that, while the abundance enhancement inferred in NGC3783 is modest, the X-ray analysis of some other objects has found extreme iron abundances. We introduce the hypothesis that the radiative levitation of iron ions in the innermost regions of radiation-dominated AGN disks can enhance the photospheric abundance of iron. We show that radiative levitation is a plausible mechanism in the very inner regions of high accretion rate AGN disks. © © 2012. The American Astronomical Society. All rights reserved..


Park K.H.,University of Maryland University College | Park K.H.,Carnegie Mellon University | Ricotti M.,University of Maryland University College | Ricotti M.,Joint Space Science Institute JSI
Astrophysical Journal | Year: 2013

In this third paper of a series, we study the growth and luminosity of black holes (BHs) in motion with respect to their surrounding medium. We run a large set of two-dimensional axis-symmetric simulations to explore a large parameter space of initial conditions and formulate an analytical model for the accretion. Contrary to the case without radiation feedback, the accretion rate increases with increasing BH velocity v bh reaching a maximum value at v bh = 2c s, in 50 km s-1, where c s, in is the sound speed inside the "cometary-shaped" H II region around the BH, before decreasing as when the ionization front (I-front) becomes R-type (rarefied) and the accretion rate approaches the classical Bondi-Hoyle-Lyttleton solution. The increase of the accretion rate with v bh is produced by the formation of a D-type (dense) I-front preceded by a standing bow shock that reduces the downstream gas velocity to transonic values. There is a range of densities and velocities where the dense shell is unstable producing periodic accretion rate peaks which can significantly increase the detectability of intermediate-mass BHs. We find that the mean accretion rate for a moving BH is larger than that of a stationary BH of the same mass if the medium temperature is T ∞ < 10 4 K. This result could be important for the growth of seed BHs in the multi-phase medium of the first galaxies and for building an early X-ray background that may affect the formation of the first galaxies and the reionization process. © 2013. The American Astronomical Society. All rights reserved.


Zoghbi A.,University of Maryland University College | Zoghbi A.,Joint Space Science Institute JSI | Reynolds C.,University of Maryland University College | Reynolds C.,Joint Space Science Institute JSI | Cackett E.M.,Wayne State University
Astrophysical Journal | Year: 2013

Timing techniques are powerful tools to study dynamical astrophysical phenomena. In the X-ray band, they offer the potential of probing accretion physics down to the event horizon. Recent work has used frequency- and energy-dependent time lags as tools for studying relativistic reverberation around the black holes in several Seyfert galaxies. This was achieved due to the evenly sampled light curves obtained using XMM-Newton. Continuously sampled data are, however, not always available and standard Fourier techniques are not applicable. Here, building on the work of Miller et al., we discuss and use a maximum likelihood method to obtain frequency-dependent lags that takes into account light curve gaps. Instead of calculating the lag directly, the method estimates the most likely lag values at a particular frequency given two observed light curves. We use Monte Carlo simulations to assess the method's applicability and use it to obtain lag-energy spectra from Suzaku data for two objects, NGC 4151 and MCG-5-23-16, that had previously shown signatures of iron K reverberation. The lags obtained are consistent with those calculated using standard methods using XMM-Newton data. © 2013. The American Astronomical Society. All rights reserved.


Kara E.,Institute of Astronomy | Fabian A.C.,Institute of Astronomy | Cackett E.M.,Wayne State University | Uttley P.,University of Amsterdam | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

We use archivalXMM-Newton observations of Ark 564 and Mrk 335 to calculate the frequencydependent time lags for these two well-studied sources. We discover high-frequency Fe K lags in both sources, indicating that the red wing of the line precedes the rest-frame energy by roughly 100 and 150 s for Ark 564 and Mrk 335, respectively. Including these two new sources, Fe K reverberation lags have been observed in seven Seyfert galaxies. We examine the low-frequency lag-energy spectrum, which is smooth, and shows no feature of reverberation, as would be expected if the low-frequency lags were produced by distant reflection offcircumnuclear material. The clear differences in the low- and high-frequency lag-energy spectra indicate that the lags are produced by two distinct physical processes. Finally, we find that the amplitude of the Fe K lag scales with black hole mass for these seven sources, consistent with a relativistic reflection model where the lag is the light travel delay associated with reflection of continuum photons offthe inner disc. ©2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Zoghbi A.,University of Maryland University College | Zoghbi A.,Joint Space Science Institute JSI | Reynolds C.,University of Maryland University College | Reynolds C.,Joint Space Science Institute JSI | And 4 more authors.
Astrophysical Journal | Year: 2013

Several X-ray observations have recently revealed the presence of reverberation time delays between spectral components in active galactic nuclei. Most of the observed lags are between the power-law Comptonization component, seen directly, and the soft excess produced by reflection in the vicinity of the black hole. NGC 4151 was the first object to show these lags in the iron K band. Here, we report the discovery of reverberation lags in the Fe K band in two other sources: MCG-5-23-16 and NGC 7314. In both objects, the 6-7 keV band, where the Fe Kα line peaks, lags the bands at lower and higher energies with a time delay of 1 ks. These lags are unlikely to be due to the narrow Fe Kα line. They are fully consistent with reverberation of the relativistically broadened iron Kα line. The measured lags, their time scale, and spectral modeling indicate that most of the radiation is emitted at 5 and 24 gravitational radii for MCG-5-23-16 and NGC 7314, respectively. © 2013. The American Astronomical Society. All rights reserved..


Sanfrutos M.,CSIC - National Institute of Aerospace Technology | Miniutti G.,CSIC - National Institute of Aerospace Technology | Agis-Gonzalez B.,CSIC - National Institute of Aerospace Technology | Fabian A.C.,Institute of Astronomy | And 4 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

We present results obtained from the time-resolved X-ray spectral analysis of the Narrow- Line-Seyfert 1 galaxy SWIFT J2127.4+5654 during a ~130 ks XMM-Newton observation. We reveal large spectral variations, especially during the first ~90 ks of the XMM- Newton exposure. The spectral variability can be attributed to a partial eclipse of the X-ray source by an intervening low-ionization/cold absorbing structure (cloud) with column density NH = 2.0+0.2 -0.3 × 1022 cm-2 which gradually covers and then uncovers the X-ray emitting region with covering fraction ranging from zero to ~43 per cent. Our analysis enables us to constrain the size, number density and location of the absorbing cloud with good accuracy. We infer a cloud size (diameter) of Dc ≤ 1.5 × 1013 cm, corresponding to a density of nc ≥ 1.5 × 109 cm-3 at a distance of Rc ≥ 4.3 × 1016 cm from the central black hole. All of the inferred quantities concur to identify the absorbing structure with one single cloud associated with the broad line region of SWIFT J2127.4+5654. We are also able to constrain the X-ray emitting region size (diameter) to be Ds ≤ 2.3 × 1013 cm which, assuming the black hole mass estimated from single-epoch optical spectroscopy (1.5 × 107Mo), translates into Ds ≤ 10.5 gravitational radii (rg) with larger sizes (in rg) being associated with smaller black hole masses, and vice versa. We also confirm the presence of a relativistically distorted reflection component off the inner accretion disc giving rise to a broad relativistic Fe K emission line and small soft excess (small because of the high Galactic column density), supporting the measurement of an intermediate black hole spin in SWIFT J2127.4+5654 that was obtained from a previous Suzaku observation. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

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